The nozzle is the part that guides the water into the runner.
The runner will work most efficiently if all the water hits its
circumference at the proper entrance angle (see box 4.7).
The bent side (see fig. 4.15 and fig.
4.17) has a special curved form to achieve this.

The 4 sides of the nozzle can be made from 2 mm mild steel.
This is easy to cut and bend, while it is just thick enough for
electric arc welding using 2.5 mm rods. If 2 mm steel is not
available, thicker steel can be used. Then make the nozzle in
such a way that the inner dimensions remain the same so that the
flow and power output will still fit with the characteristics
given in par. 4.1.

The runner side and bent side are just rectangular pieces, see
fig. 4.15 for the dimensions. The free side and alternator side
have a more complicated form which can be copied onto the
material in the same way as with the side disks: Make copies of
fig. 4.15, glue them onto the steel sheet and mark the relevant
points with a centre punch. Arrange the 2 pieces of paper in such
a way on the steel that the centre of the runner can also be
marked since this makes it easier to mark the inner radius with
compasses or the modified vernier callipers.

Fig. 4.15: Sides of the nozzle.

As cut out, the alternator side and free side have a radius of
37.5 mm, leaving no clearance with the runner. When fitting the
assembled nozzle onto the runner, these edges will be filed off
or grinded off a little until it fits well with only a small
clearance. In this way, leakage of water through this clearance
will be minimal and thus efficiency will be best.

When alternator side and free side are cut to shape as
described above, welding them onto the bent side may become
tricky since near the tip, there is so little material left. Then
the whole tip may melt and end up in a large droplet of steel,
meaning that the carefully designed shape is lost. So when
cutting out the free side and alternator side, better leave a
lump of material near the tip (not drawn in fig. 4.15. This edge must be filed off before
assembling the runner sides. Having this rounded edge is not
essential but without it, the charger will consume roughly 10 %
less flow than calculated in par. 4.1 and consequently power
output will be 10 % lower (but it might still be higher than
expected if overall efficiency turns out to be better than
expected).

When making the sides, take care not to damage the inside
surfaces. This is especially important for the areas near the
runner, where water will have very high velocities and any
disturbances will cause high friction losses. So for bending the
bent side, do not hammer directly at the inside surface. Better
find a piece of pipe that has about the right radius and hammer
the tip of the bent side around it while holding a heavy object
against the other end. Use the free side or alternator side as a
reference. For easy welding, the bent side should fit closely
against the free side and alternator side. This might take quite
a while and if it looks too bad, hammer it flat and try again.
Bending it to a perfect fit is nearly impossible so for welding,
have it clamped against the alternator side and bent side.

The free side has a hole in it through which the blocking
timber can be fixed with a wood screw. When there is no blocking
timber, this hole should be closed and therefor an M6 thread is
tapped into it so that a short bolt fits into it. When assembling
the four sides of the runner, check with the runner which side
will become the free side. This depends on the direction of
rotation of the alternator.

The shape of a blocking timber resembles closely the shape of
the alternator- or free side of the nozzle. In fig. 4.16, two
shapes of blocking timber are drawn. The difference between the
two is that the more complicated type guides the water right up
to the tip of the nozzle. This means that the water jet coming
from the nozzle will be equally wide everywhere and therefor the
force exerted on a runner blade will be constant.

Fig. 4.16: Two possible shapes for a blocking timber.

With the simple wedge-shaped type, the water jet is not guided
all the way. Once the water jet has passed the edge of the
blocking timber, it can expand in width as the bent side tries to
deflect it towards the runner. This means that near the tip of
the nozzle, runner blades are exposed to a wider water jet (in
axial direction) and thus to larger forces than expected based on
the thickness of the blocking timber. Therefor the more
complicated type (top drawing in fig. 4.16) is needed when forces
on blades are becoming critical, so at a head of 15 m or higher.
Because it guides the water jet better, this type will also give
a slightly higher efficiency.

A demonstration charger that will be installed temporarily at sites with different heads.

When available flow is less than the charger needs. Then one could adjust the nozzle such that it takes just a bit less flow than the canal provides so that the penstock remains full of water and the charger produces some power. Without reducing the flow, air would enter the penstock pipe, the charger would operate at a reduced head and a reduced flow and power output would be minimal.

The space between the alternator side and free side must be 51
mm (nozzle width is 51 mm). The bent side and runner side are 53
mm wide so at each end, they overlap 1 mm with the alternator
side and free side. This way the bent side and runner side
overlap enough to make assembly easy, while still there is enough
space left open to make a strong weld that penetrates nearly the
whole thickness of the material.

Assembling the 4 sides is a job that is best done by 2 people.
One can hold two parts in proper position with respect to one
another while the other makes two small welds just to fix them.
For easy, accurate working, sides can be clamped onto a block of
steel or wood with a right angle. Especially for welding the bent
side, it is a great help to have someone press it down so that
the seam closes completely. Only when all sides are fixed and all
angles are checked, the seams can be welded completely.

Fig. 4.17: Nozzle sides assembled.

Onto the assembled runner sides, an extension pipe can be
welded that serves the following purposes:

It forms the connection to the frame.

It forms the transition from a round cross section of the
penstock pipe to the rectangular cross-section of the
nozzle itself.

It provides a connection that can be taken loose easily
in order to fit or remove the blocking timber, or have
the charger fitted to another penstock pipe. This makes
that all chargers fit to different sizes of penstock
pipes so chargers are interchangeable.

The easiest way is to use a piece of 2.5" pipe with a 2.5"
conical pipe thread cut into it on one end, see fig. 4.18. Such
pieces of pipe with screw thread are made to order by specialised
workshops. In the Philippines, hardware shops sold `standpipes'
that consisted of a short length of pipe with thread at both
ends, which were long enough to cut into two and use both ends.
Or maybe somewhere there is a long length of pipe with screw
thread at the ends that serves no purpose and the owner will
allow you to cut it off. For an alternative if such a pipe cannot
be found, see box 4.12.

For making the rectangular cross section, the pipe is cut in
some 10 mm lengthwise at the places where the corners will come.
These cuts will make that the pipe will bend easier there. To
make sure that the screwthread end will retain its shape during
hammering, screw the socket (see below) onto it. Find a heavy
hammer, hold the pipe over the wedge-shaped point of an anvil (or
another heavy object) and hammer on the triangular areas that
should become flat, see fig. 4.18. Once it fits well, the nozzle
itself can be welded onto it and the lengthwise cuts have to be
welded again. If the pipe is galvanised, first file off the zinc
layer up to 10 mm from the weld itself to prevent poisonous fumes
to come off. The same goes for welding on the socket, if that was
galvanized.

Fig. 4.18: The extension pipe.

Now a 2.5" socket can be screwed onto the nozzle and on
this socket, an especially made piece of pipe can be welded that
fits tightly into the PE (Poly-Ethylene, a kind of plastic)
penstock pipe. If the size of the penstock pipe is known already,
this piece can be made right away. Often PE pipe is not
completely round so measure the largest and smallest diameter and
take the mean to find an accurate figure. Multiply this by 3.14
to find the circumference. Cut out a piece of 2 mm steel sheet of
about 100 mm wide and as long as the circumference that was just
calculated. Bend it round, weld the lengthwise seam and carefully
file it flat to prevent leakage. If the diameter of this pipe
differs too much from that of the socket, it can not be welded
onto the socket directly. Then make a ring of ca. 8 mm steel rod
that bridges the gap between them and weld the 3 parts together.
To make it easier to fix or take loose the socket from the
charger, one could weld handles onto it. Take care to make only
light welds since welding at one point will make it lose its
shape. In fact one small piece of steel welded on somewhere
around the circumference is already enough. One could hook on a
rope there, wind it round the socket one turn and fix it to a
long piece of wood. Now the piece of wood can be used as a lever
for turning the socket.

Because of the thickness of the steel sheet itself, the piece
of pipe onto which the PE pipe will be fixed, will have an outer
diameter that is 2 mm larger than the inner diameter of the PE
pipe. This assures a good tight fit but it can be difficult to
get it into the penstock pipe. So bevel the end and also the
inside edge of the penstock pipe. If it still doesn't go in far
enough, heat up the PE pipe in hot water or hold a piece of board
over the socket and hammer it into the PE pipe.

Disadvantages of a screwthread connection are:

It could be quite hard to remove the socket once the
screwthread has become oxidized. So the screwthread
should always be greased before fitting the socket.

Maybe such a piece of pipe with a ready made screwthread
is hard to get or too expensive, see box 4.12.

Instead of using 2.5" pipe
with a ready made pipe thread, one could make flanges,
see fig. 4.19. Flanges of 3 mm thick steel sheet, an
outer radius of 60 mm and 6 M6 bolts at a radius of 50 mm
should do the job. To make it waterproof, fit some layers
of thick paper in between. The flange on the nozzle
should have an inner radius of 38.2 mm (or 36.7 mm if you
make the extension pipe out of 2 mm steel sheet, see
below). The inner radius of the other flange follows the
radius of the piece of pipe onto which the penstock pipe
is fitted. Have the pipes stick into the flanges only
about 1 mm. In this way, they can be welded both at the
outside and at the inside.

To connect the nozzle to its flange, still a piece
of 2.5" pipe could be used and then this should be
cut in lengthwise and hammered to a rectangular cross
section like described above. But now a piece of only 65
mm long will do since there is no screw thread that can
get deformed when bending it to a rectangular cross
section

Instead of 2.5" pipe, one could also make a
piece of pipe from a piece of 2 mm (or thicker) steel of
65 x 224 mm. Plan on having the seam right through the
middle of one of the 4 triangular flat areas. Then
measure off where the corners of the nozzle itself will
end up and draw the triangular areas that should remain
flat. Bend it to shape by hand over a protruding piece of
steel. The lines in fig. 4.18 show where the strip should
bend in order to get a round cross section at the flange
side. With 2 mm steel, there is little need to cut it in
at the corners in order to have it bend easier but there
is no harm in it either. Making this piece of pipe from
steel sheet has the added advantage that the charger will
end up a little lighter and more compact.

Fig. 4.19:A flanged connection, please note:
Not on scale 1:1.

Making a tricky connection just to keep chargers
interchangeable might seem a bit ridiculous if this is the first
charger to be built and there is no other one within thousands of
km. Still it is worthwhile to think ahead, maybe in 2 years time
there are quite a few running. Also chargers will be are
installed in remote villages where no welding can be done. Then
it is handy if a spare charger could be fitted to the penstock
pipe if the first one needs repair.

Another reason for such a removable connection is that with
small penstock pipes, it might be difficult to fit and remove a
blocking timber through the narrow piece of pipe where the
penstock pipe fits on. Small size penstock pipes can only be used
at quite high head and under these conditions, the widest
blocking timber is needed.

To keep chargers interchangeable, of course all chargers in
one area should have either a screwthread and socket connection
or a flanged connection.